Deleted unnecessary descriptions

Author: SakiTakamachi

reference/bc/bcmath/number/pow.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<refentry xml:id="bcmath-number.pow" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">
+<refentry xml:id="bcmath-number.pow" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
  <refnamediv>
   <refname>BcMath\Number::pow</refname>
   <refpurpose>Raises an arbitrary precision number</refpurpose>